Surface textures, e.g., three-dimensional patterns, may be imparted to web materials by a process in which a web is coated with a curable coating, a texture is imparted to the curable coating by a replicative surface, e.g., an engraved metal roll, and the coating is cured while in contact with the roll by passing radiation through the web.
The web materials resulting from this process may be used as release webs in processes in which a plastic film is formed (e.g., cast) on or against a release web, and then separated from the release web after cooling or curing to set the plastic material. The release web provides a surface from which the set plastic material can be readily separated and imparts to the surface of the plastic material the texture of the release surface. For example, a desired textured surface can be provided on the surface of a plastic sheet material by forming the plastic material on or against a release web having a textured surface that is the mirror image of the desired textured surface.
U.S. Pat. Nos. 4,289,821 and 4,322,450, the disclosures of which are incorporated herein by reference, disclose techniques for producing surface effects in a release coating on a release web for use in casting processes. One method disclosed comprises applying a coating of an electron beam radiation curable material to one surface of a web substrate, pressing the coated side of the substrate against a replicative surface, e.g., an engraved metal roll, irradiating the coating with electron beam radiation to cure the coating, and stripping the substrate from the replicative surface with the cured coating adhered to the substrate. Using these methods the replicative surface can be reproduced in the cured coating with essentially 100% fidelity. Other replicative casting processes are disclosed in U.S. Pat. Nos. 6,355,343 and 7,964,243, the disclosures of which are incorporated by reference herein.
Replicative casting processes can be used to form very fine, even nanoscale, textures. One example of a micro-scale texture is referred to in the art as “Sharklet.” Sharklet textures can be applied to plastic sheet products to provide the products with a surface that is structured to impede bacterial growth. The micro-scale texture of the surface replicates sharkskin denticles, which are arranged in a diamond pattern with millions of tiny ribs. Sharklet materials are discussed, for example, in U.S. Pat. Nos. 7,650,848 and 8,997,672, the complete disclosures of which are incorporated herein by reference. Such materials are important in providing non-toxic bioadhesion control and antifouling properties, and have been proposed for use in the medical device industries. Other micro-scale textures include lenticular lens textures, drag reduction textures (e.g., Riblet features), and cube corner textures that create a reflective surface.
Nano-scale textures include diffraction gratings, hydrophobic surfaces (e.g., lotus leaf like surfaces having a micro- and nanoscopic architecture on the surface that minimizes the adhesion of a droplet adhesion to the surface), and laser interference rainbow patterns, which display reflected light as colors of the visual spectrum. One example of a nanoscale texture is a diffraction grating that has a series of raised ridges about 400 nm wide, spaced approximately 800 nanometers apart, with a depth of approximately 100 nm.